Method for producing injection molded and centrally apertured disc records

ABSTRACT

Heated material is injected into an annular cavity, defined by a pair of mold-halves, through a sprue passage, defined by a sprue bushing and an end portion of a punch. The annular cavity and the sprue passage form, respectively, the centrally apertured part and a sprue. After partial cooling of the heated material, the punch is locked in place while the annular cavity is displaced relative to the sprue passage so that the sprue is severed from the part along the peripheral surface of the punch end portion. The mold halves are separated to open the annular cavity while the sprue is resting on the punch end portion, and while the part is held by the punch end peripheral surface. After the mold halves are separated, a sprue ejector member and a part ejector member are actuated to eject, respectively, the sprue and the part from the punch end portion.

This is a division of U.S. Pat. application Ser. No. 642,162, filed Dec.18, 1975, and now U.S. Pat. No. 3,989,436.

This invention relates generally to method and apparatus for molding acentrally apertured part; and, more particularly, concerns method andapparatus for injection molding a centrally apertured and spirallytracked record, such as a video disc.

While this invention is described herein in the context of an apparatusfor injection molding video discs, it has applications in other areaswhere it is important to have the center hole substantially concentricwith the recorded spiral track on the surface of the record: forexample, stereo and quadraphonic LP records.

In certain video disc systems, video information is recorded in the formof geometric variations in the bottom of a spiral track on the surfaceof a centrally apertured record. For playback, the record is mounted ona rotatable turntable having a spindle which engages the record aperturefor centering, and, then relative motion is established between therecord and a stylus riding in the track. Electrical circuitry serves totranslate the variations detected by the track-riding stylus into asignal for effecting a visual display of the recorded video information.A system of the above-mentioned type is described in U.S. Pat. No.3,842,194 issued to J. K. Clemens.

In such video disc systems, it has been recognized that, not only theaverage speed of relative motion between the stylus and the record mustbe maintained at a predetermined speed (e.g., 450 rpm), but the cyclicalvariations about the average speed must be limited, for proper playback,within specified tolerance limits (e.g. ±0.01 percent). It is desirableto reduce the cyclical speed variations to assure that the synchronizingpulses in the recovered television signal are fairly stable and withinthe lockup range of the deflection circuits of a television receiver.The cyclical speed variations are particularly unpleasant where therecorded information is a color television signal.

One of the sources of cyclical speed variations is the recordeccentricity. For proper playback of the video disc, it is importantthat the replicated record's center hole is concentric with the spiralgroove center to a high degree of accuracy.

The concentricity between the record center hole and the record spiraltrack is particularly important (1) where the record playback speed isrelatively high (e.g., 450 rpm), (2) where the record groove density isrelatively high (e.g., 5,555 gpi), and (3) where the bandwidth of therecorded signal is relatively high (e.g., 4.3 to 6.3 MHz).

Pursuant to the principles of the present invention, an injectionmolding technique with an in-mold punching feature is disclosed forreplicating centrally apertured and spirally tracked records to assureconcentricity to a high degree. An excellent concentricity is obtainedbecause both operations, the molding of the part and the punching of thesprue to form the center hole therein, are performed in a single set-up.

For production of a record without any flow lines and other surfacedefects in the recorded region, it is important to inject the plasticmaterial into the mold cavity at the center. Therefore, the use of acore/plug arrangement to form a center-hole in the record is notpractical. Pursuant to the principles of the present invention, a novelarrangement for forming the center hole in the record is disclosed.

Additionally, for production of a record without any flow lines andother surface defects in the recorded region, solidified particles frompreviously injected shots cannot be tolerated in subsequent shots.Pursuant to the principles of the present invention, a novel arrangementfor sprue removal, which prevents appearance of solidified particles inthe injected shots, is disclosed. Further, it is desirable that thesprue removal arrangement must be suitable for producing a record havinga relatively large center hole (e.g., 11/2 and one-half inch).

A first mold-half and a second mold-half are reciprocably mounted to aplaten. A sprue bushing having an opening in communication with aninjection nozzle is secured to the platen. A punch, having an endportion in registry with the sprue bushing, is reciprocably mountedrelative to the second mold-half. When the second mold-half is in aclosed location, (1) the punch end portion and the opening in the spruebushing define a sprue passage, and (2) the first and the second moldhalves define an annular cavity surrounding the sprue passage. Theannular cavity and the sprue passage form, respectively, the centrallyapertured part and the sprue when heated material is injected therein.After partial cooling of the heated injected material, the first and thesecond mold halves move from the closed location to a locationintermediate of the closed location and an open location while the punchis locked in place to sever the sprue from the part along the peripheralsurface of the punch end portion. A portion of the first mold-half,where the punch end portion enters, serves as a die. The mold halves arethereafter separated to open the annular cavity while the sprue isresting on the punch end portion, and while the part is held by thepunch end peripheral surface. After the mold halves are separated, asprue ejector member and a part ejector member are actuated to eject,respectively, the sprue and the part from the punch end portion.

In the accompanying drawings in which like reference characters refer tosimilar parts:

FIG. 1 is a partly schematic, sectioned elevation view of an injectionmolding apparatus for replicating centrally apertured and spirallytracked records pursuant to the principles of the present invention;

FIGS. 2-7 illustrate a sequence of operations executed by the injectionmolding apparatus of FIG. 1 for replication of records; and

FIG. 8 illustrates an arrangement for limiting the stroke of a firstmold-half between a closed location and an intermediate location.

Referring to the drawings, a platen 10 and a spacer plate 11 are securedto a frame 12 of an Injection molding machine. A sprue bushing 13 havingan opening 14 which communicates with an injection nozzle 15 is securedto the platen 10. First bearing means support a reciprocal motion of afirst mold half 16 relative to the platen 10 between a closed location(FIG. 1) and an intermediate location (FIGS. 2-7). The first bearingmeans includes a set of guide pins 17 (e.g., 4) spacedly secured to themachine frame 12. The first mold-half 16 has a set of openings 18through which the guide pins 17 are inserted.

Second bearing means support a reciprocal motion of a second mold-half19 relative to the platen 10 between a closed location (FIG. 1), and anopen location (FIGS. 6 and 7). In this embodiment, the guide pins 17also serve as the second bearing means. The second mold-half 19 also hasa set of openings 20 through which the guide pins 17 are inserted.

Third bearing means support reciprocal motion of a punch 21 relative tothe second mold-half 19 between a first position (FIGS. 1 and 7) and asecond position (FIGS. 2-6). The third bearing means includes a secondset of guide pins 22 secured to a second mold-half carrier 23. A punchcarrier 24, which carries the punch 21, has a set of openings 25,through which the guide pins 22 are inserted.

First selectively actuated means 26 cause motion of the second mold-halfbetween the closed location (FIG. 1) and the open location (FIGS. 6 and7). The first selectively actuated means 26 comprises a piston 27 ridingin a cylinder 28. A connecting rod 29 connects the piston 27 to anisolation plate 30 which is secured to the second mold-half carrier 23.Pressurized fluid is admitted into the cylinder 28 through a fluid valveF1 to move the second mold-half 19 from the closed loaction (FIG. 1) tothe open location (FIGS. 6 and 7). Pressurized fluid is admitted intothe cylinder 28 through a fluid valve F2 to move the second mold-half 19from the open location (FIGS. 6 and 7) to the closed location (FIG. 1).

When the first and the second mold halves (16 and 19) are in the closedlocation (FIG. 1), (1) an end portion 31 of the punch 21 and the spruebushing opening 14 define a sprue passage, and (2) the first and secondmold halves define an annular cavity surrounding the sprue passage. Theannular cavity and the sprue passage form, respectively, a centrallyapertured part 32 and a sprue 33 when heated material (e.g., rigid PVCblend) is injected therein.

Second selectively actuated means 34 cause motion of the first mold-half16 with the second mold-half 19 in response to motion of the secondmold-half from the closed location (FIG. 1) to a location which isintermediate (FIG. 2) of the closed location and an open location (FIGS.6 and 7) whereby the annular cavity remains closed while the first andthe second mold halves move from the closed location to the intermediatelocation. The second selectively actuated means 34 comprises a piston61, in the form of an annular ring, riding in a cylinder 62, in the formof an annular recess in the platen 10. Pressurized air is admitted inthe cylinder 62 through an air valve A3 to move the first mold-half 16from the closed location (FIG. 1) to the intermediate location (FIGS.2-7).

FIG. 8 illustrates an arrangement for limiting the stroke of the firstmold-half 16 between the closed location (FIG. 1) and the intermediatelocation (FIGS. 2-7). A sleeve 70 is secured to the platen 10 by a bolt71. The sleeve 70 has a shank portion 72 which passes freely in anopening 73 in the first mold-half 16. The distance between a headportion 74 of the sleeve 70 and a base-plate 75 of the first mold-half16 limits the stroke of the first mold-half between the closed location(FIG. 1) and the intermediate location (FIGS. 2-7).

Third selectively actuated means 35 lock the punch in place while thefirst and second mold halves (16 and 19) move from the closed location(FIG. 1) to the intermediate location (FIG. 2) whereby the sprue 33 issevered from the part 32 along the peripheral surface of the punch endportion 31. A portion of the first mold-half 16 where the punch endportion 31 enters serves as a die. Third selectively actuated drivemeans 35 comprises a piston 63 riding in a cylinder 64. A connecting rod65 connects the piston 63 to the punch carrier 24. Pressurized air isadmitted in the cylinder 64 through an air valve A4 to lock the punch 21in place while the first and second mold halves (16 and 19) move fromthe closed location (FIG. 1) to the intermediate location (FIG. 2).After the second mold-half 19 reaches the intermediate location (FIG.2), the punch carrier 24 moves with the second mold-valve from theintermediate location (FIG. 2) to the open location (FIG. 6). A spring69 is provided for returning the punch carrier 24 to the first position(FIGS. 1 and 7) after the part 32 is ejected (FIG. 6).

As illustrated in FIG. 3, the first and the second mold-halves areseparated to open the annular cavity while the sprue 33 is held in anundercut 36 in the punch end portion 31, and while the part 32 isresting on the punch end peripheral surface.

As illustrated in FIGS. 3, 4 and 5, first means 37 are provided forejecting the sprue 33 from the punch end portion 31 after the sprue issevered. The first sprue ejecting means 37 includes a first sprueejector member 38 mounted in an opening in the punch end portion 31 formovement toward and away from a retracted position (FIGS. 3 and 5).Fourth selectively actuated means 39 advances the first sprue ejectormember 38 away from the retracted position (FIG. 3) to an advancedposition (FIG. 4) so as to eject the sprue 33 from the punch end portion31. Pressurized air is admitted in a cylinder 66 through an air valve A5to advance the sprue ejector member 38 away from the retracted position(FIG. 3). A spring 40 is provided for returning the first sprue ejectormember 38 to the retracted position (FIG. 5) after sprue ejection (FIG.4).

In one embodiment of the present invention, ejection of the sprue 33from the punch end portion 31 by the first sprue ejecting means 37,after the sprue is severed, leaves the sprue in the sprue bushing 13 asshown in FIG. 4. As illustrated in FIGS. 4, 5 and 6, second means 41 areprovided for ejecting the sprue 33 from the sprue bushing 13 after theejection of the sprue from the punch end portion 31. The second sprueejecting means 41 includes a second sprue ejector member 42 mounted inan opening in the sprue bushing 13 for movement toward and away from awithdrawn position (FIGS. 4 and 6). Fifth selectively actuated means 43advances the second sprue ejector member 42 away from the withdrawnposition (FIG. 4) to an advanced position (FIG. 5) so as to launch thesprue 33 from the sprue bushing 13. Pressurized air is admitted in acylinder 67 through an air valve A6 to advance the sprue ejector member44 away from the withdrawn position (FIG. 4). A spring 44 is providedfor returning the second sprue ejector member 42 to the retractedposition (FIG. 6) after sprue launching (FIG. 5).

As illustrated in FIGS. 5, 6 and 7, the apparatus further includes means45 for ejecting the part 32 from the punch end peripheral surface aftersprue ejection. The part ejecting means 45 comprises a part ejectorsleeve 46 which is mounted in an opening in the second mold-halve 19 formovement toward and away from a retarded position (FIGS. 5 and 7). Sixthselectively actuated means 47 advances the part ejector sleeve 46 awayfrom the retarded position (FIG. 5) to an advanced position (FIG. 6) soas to eject the part 32 from the punch end peripheral surface.Pressurized air is admitted in a cylinder 68 through an air valve A7 toadvance the part ejector sleeve 46 away from the retarded position (FIG.5). Bayonet hooks 48 are provided for returning the part ejector sleeve46 to the retarded position (FIG. 7) after part ejection (FIG. 6). Afterthe molded part 32 is ejected, as shown in FIG. 7, the part drops in achute 49 which is inserted between the first and second mold halves (16and 19) when the mold halves are fully open (FIGS. 6-7). While the chute49 is provided for collecting the molded part 32 in this particularembodiment, other transfer means, such as a pickup arm, may be used tocollect the molded parts.

As illustrated in FIGS. 6 and 7, the spring 69 returns the punch carrier24 to the first position (FIG. 7) after the part 32 is ejected. Thebayonet hooks 48 provided on the punch 21, which is secured to the punchcarrier 24, engage the projections 76 on the selectively actuated means47 to return the selectively actuated means 47 and the sleeve 46 to theretarded position (FIG. 7).

Where the centrally apertured part is a disc record, each of the firstand second mold halves (16 and 19) includes an annular stamper 50 whichis secured to a plate 51 by a set of hold down rings 52. Each of theannular stampers 50 is coined at the inner and outer peripheralsurfaces. The hold down rings 52 secure the coined peripheral surfacesof a respective one of the annular stampers 50 to a respective one ofthe plates 51. A respective one of the hold down rings 52 is bolted to arespective one of the plates 51.

A channel 54 is provided on the surface of each of the plates 51underneath a respective one of the stampers 50. Air is evacuated fromthe surface channels 54 through vacuum valves V5 and V6 to assure thatthe stampers 50 are flatly and securely held by the respective plates51.

The sprue bushing 13 further includes a subsurface channel 56 forcirculating water therethrough (at 70° F.) to maitain the sprue bushingat a temperature which facilitates the severance of the sprue 33 fromthe part 32. Water is admitted in the subsurface channel 56 through awater valve W1.

The punch 21 further includes a subsurface channel 57 for circulatingwater therethrough to maintain the punch end portion 31 at thetemperature which facilitates the severance of the sprue 33 from thepart 32. Water is admitted in the subsurface channel 57 through a watervalve W2.

Air is evacuated from the annular cavity and the sprue passage throughvacuum valves V1, V2, V3, and V4 to facilitate injection of plasticmaterial into the annular cavity.

Each of the plates 50 further includes a subsurface channel 59 forcirculating water therethrough so as to maintain a respective one of themold halves (16 and 19) at a certain desirable temperature for injectionmolding of the parts. Water is admitted in the subsurface channels 59through water valves W3 and W4.

It is important to note that a high degree of concentricity between therecord spiral track and the record center hole is obtained because bothoperations, the formation of the spirally tracked record and punching ofthe sprue to define the record center hole, are performed in a singleset-up. A master, from which the stamper is generated, has a circulartrack near the outer periphery which is very accurately positionedrelative to the recorded spiral track. When the stamper is replicatedfrom the master, both the circular track and the recorded spiral trackare transferred to the stamper. In the blanking and coining operation,the circular track on the stamper is used to precisely center the innerand the outer coined surfaces on the stamper with respect to therecorded spiral track. In the set-up, the inner and the outer coinedsurfaces on the stamper cooperate with the corresponding mating surfaceson the mold to obtain highly accurate positioning of the stamper on themold. Similarly, the punch peripheral surface which defines the recordcenter hole is very precisely located relative to the mating surfaces onthe mold. Since both the stamper, which forms the record spiral track,and the punch peripheral surface, which defines the record center hole,are very carefully aligned with respect to the mold, a high degree ofconcentricity between the record spiral track and the record center holeis obtained.

What is claimed is:
 1. A method for forming a disc record having anannular recorded region surrounding a centering aperture therein; saidmethod comprising the steps of:(A) injecting heated material into anannular cavity defined by a pair of mold halves through a sprue passagelocated at the center of said annular cavity and defined by a spruebushing and an end portion of a punch; and said annular cavity and saidsprue passage forming, respectively, said centrally apertured record anda sprue; (B) locking said punch in place while said annular cavity isdisplaced relative to said sprue passage so that said sprue is severedfrom said record along the peripheral surface of said punch end portion;(C) separating said mold halves to open said annular cavity while saidsprue is resting on said punch end portion and while said record is heldby said punch end peripheral surface; (D) actuating a sprue ejectormember to eject said sprue from said punch end portion; and (E)actuating a record ejector member to eject said record from said punchperipheral surface.
 2. A method for forming a disc record having anannular recorded region surrounding a centering aperture therein; saidmethod comprising the steps of:(A) injecting heated material into anannular cavity defined by a pair of mold halves through a sprue passagelocated at the center of said annular cavity and defined by a spruebushing and an end portion of a punch; and said annular cavity and saidsprue passage forming, respectively, said centrally apertured record anda sprue; (B) locking said punch in place while said annular cavity isdisplaced relative to said sprue passage so that said sprue is severedfrom said record along the peripheral surface of said punch end portion;(C) separating said mold halves to open said annular cavity while saidsprue is resting in said sprue bushing and while said record is held bysaid punch end peripheral surface; (D) actuating a sprue ejector memberto eject said sprue from said sprue bushing; and (E) actuating a recordejector member to eject said record from said punch peripheral surface..Iadd.
 3. A method for forming a disc record having an annular recordedregion surrounding a centering aperture therein, said method comprisingthe steps of: (A) injecting heated material into an annular cavitydefined by a pair of mold halves through a sprue passage located at thecenter of said annular cavity and defined by a sprue bushing and an endportion of a punch; and said annular cavity and said sprue passageforming, respectively, said centrally apertured record and a sprue; (B)displacing said annular cavity relative to said punch so that said sprueis severed from said record along the peripheral surface of said punchend portion; (C) separating said mold halves to open said annular cavitywhile said sprue is resting on said punch end portion; and (D) removingsaid sprue from the punch end portion and said record from between themold halves. .Iaddend..Iadd.
 4. A method in accordance with claim 3 inwhich the sprue is severed from the record by locking the punch in placeand displacing the annular cavity relative to the sprue passage..Iaddend..Iadd.
 5. A method in accordance with claim 4 in which therecord is held by the punch end peripheral surface when the mold halvesare separated. .Iaddend..Iadd.
 6. A method in accordance with claim 5 inwhich the sprue is removed from the punch end portion by actuating asprue ejection member. .Iaddend.